Battery-powered devices often monitor the status of the battery and indicate a low battery status as the battery approaches a fully discharged state, e.g., the end of its useful life. Devices known in the art to implement this monitoring capability include analog-to-digital converters (“A to D converters”) and coulomb counters. An A to D converter typically measures the battery's voltage with a known load. As the battery approaches a fully discharged state, the battery's voltage decreases, and the battery's status is extrapolated based on the relationship between the known load and the measured voltage. However, many devices that require low battery detection capability do not include an A to D converter, and thus these solutions require additional components, which add to the cost and complexity of the device.
A coulomb counter measures the coulombs injected into a battery versus the coulombs taken out. This device measures 1) ambient temperature using a thermistor and (2) current through a shunt resistor. A microprocessor is also required to analyze the temperature and current data. The microprocessor typically utilizes a look-up table to determine how much energy has been consumed by the battery and to extrapolate the battery's status. Coulomb counters, like A to D converters, are not present in most battery-powered devices, and thus solutions that use coulomb counters require additional components, resulting in additional cost and complexity. One object of this invention is to monitor the status of a battery within a battery-powered device, without using an A to D converter or a coulomb counter.
As described above, known methods of monitoring a battery's status may require the installation of additional components. While many battery-powered devices do not have an A to D converter or a coulomb counter, many include a microprocessor and a voltage pump. In some instances the microprocessor and the voltage pump are integrated into a single device. The voltage pump regulates the voltage output. As the battery approaches a fully discharged state, the voltage pump has to work harder to maintain the desired output voltage. Some voltage pumps use Pulse-Width Modulation (PWM), where the voltage pump is continuously operating, and the boost provided by the voltage pump is dependent upon the pulse width of a control signal to the voltage pump. Other voltage pumps are switched mode pumps that are switched on and off, where the boost provided by the voltage pump is dependent upon how often the voltage pump is on.